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Yellow Vest

Symptoms and Traits of Autism

Autism has a wide variety of symptoms and traits. This is because autism is caused by differences in brain development. Not only does the brain govern thought and emotion while absorbing input from its surroundings, it also regulates many other systems from sleep cycles to digestion. So, differences in the brain will affect the body in many ways.


Each experience of autism is unique - two individuals with autism might share some traits but not others. This is why autism is referred to as a spectrum. However, it is more complex than a linear spectrum with only two extremes. Check out Understanding the Spectrum, a webcomic by an artist with autism, for a visual description of the variable nature of the autism spectrum.

Traits that may display to varying degrees and in unique combinations in autistic children and adults:



  • have difficulty expressing their needs in words

  • have difficulty identifying and expressing their emotions

  • echo words or use repeated words in place of typical language patterns​

  • may not use vocal words at all


Social Interactions

  • avoid eye contact while speaking or listening

  • seem like they are unaware of or ignoring people when others speak to them

  • prefer not to be touched, especially if they are not the one initiating the closeness

  • not engage in pretend play or imagined play - might not enjoy "feeding" a doll

  • struggle to relate to others' emotions

  • seem uninterested in others - this might be because they are actually uninterested or because they are not sure how to communicate or interact with others



  • have heightened sensitivity to sounds, smells, or textures - they might have unusual reactions to how things feel, taste, smell, or sound

  • repeat actions including motions, sounds, and words

  • engage in activities that stimulate their senses such as making noises, flapping their hands, or rocking their bodies

  • fixation on sensory experiences they find enjoyable

  • have difficulty adapting to changes in schedule - this is more than just disappointment; they experience stress even if they would normally enjoy an activity



  • a child might not point at objects or might not follow with their eyes when someone points to something

  • a child might lose skills they once had (such as loss of vocabulary)

  • delayed language development

  • delayed cognitive or learning skills

  • may have passionate interests and learn all they can about a subject

See below for a deeper look at CommunicationSocial InteractionBehavior, and Learning and explore the connections. 


Just as communication connects different people, the act of communication requires connections between different parts of the brain. These different parts of the brain connect with each other using nerve fibers that develop during infancy and childhood. Children can first begin to hear at about 3 months prior to birth. As they listen and later practice speaking, nerve fibers grow and connect two main language areas in the brain. A lower nerve connection forms first, prior to and during infancy. An upper nerve connection forms throughout childhood. (More info here.)

The most famous language regions of the brain are Wernicke's area (which supports language comprehension by receiving information from sensory areas) and Broca's area (which coordinates motor speech by regulating breathing and vocal muscle movements), but language processing is not isolated to these regions.​

Illustration of two main language regions of the brain highlighted in orange and yellow and the path of upper and lower nerve connections in blue and green. Image Source:

​Not only are multiple regions of the brain required to complete a task, single regions of the brain also have multiple roles. Language is complex and so are the neural networks that facilitate it. (For example, the left inferior parietal lobule (IPL) and the left middle temporal gyrus (MTG) partner with Wernicke's and Broca's areas to enable language tasks (such as remembering words) but are also used in perceiving facial expressions and processing sensory information. Other frontal regions support comprehension. More info here.)

​Differences in how these regions physically develop impacts how individuals are able to communicate. A 2017 study using MRI scans examined the number of nerve connections in these language regions for individuals with autism compared to individuals without autism and found consistent differences. Individuals with ASD had fewer connections involving Wernicke's and Broca's areas than individuals without ASD but more connections involving their IPL and MTG regions than individuals without ASD. These differences remained across all age groups.  (This does not mean that the intelligence of individuals with autism is lower or higher, merely that different brains process information differently.) This article by the Hussman Institute for Autism provides a clear summary of older related studies and a helpful discussion of other ways in which differences in neural connections align with the traits of autism. 

So how do these differences connect to the symptoms of Autism? Let's revisit the list from our "About Autism" page:

  • have difficulty expressing their needs in words

    • In order to express a need, an individual must first process sensory information in order to identify the need - hunger, tiredness, boredom, etc. They must then visualize a solution for that need. A 2004 study found that individuals with autism have less activity in the sections of the brain responsible for visualizing what is described in a sentence.  Connecting sensory processing, visualization, and language is understandably challenging.

  • have difficulty identifying and expressing their emotions

    • ​Similar to the above point, this requires the coordination of separate mental tasks. Added to this is the fact that emotions are often harder to identify than physical needs because they are not as tangible and often come as mixtures rather than individually (think of being "hangry" - angry because you are hungry). This will be discussed further in the sections on social interaction and behavior.

  • echo words (called echolalia) or use repeated words in place of typical language patterns

    • Notice that the differences found by the 2017 MRI study weren't all decreases in activity. Some language areas (the IPL and MTG regions which help with remembering words) showed increased connections compared to individuals without ASD. This overstimulation of some areas can further lead to an imbalance between how brain regions work together to produce language. Some individuals with autism may only say one word at a time. Others might repeat particular phrases in multiple contexts.

  • may not use words at all

    • Some individuals with autism do not communicate verbally although they can fully receive verbal communication from others. They may be able to fully comprehend what is being said to them but their brain cannot coordinate the complex actions needed to form words in return. (This is also true of other conditions that affect Boca's area, in charge of motor speech.) Various alternative methods of communication such as manual communication boards which associate words with images that individuals can point to are available and are continually being refined to provide other avenues for communication. 

Social Interaction

Communication is about more than just connecting thoughts with words; it is also deciding when to say what to whom and which words and tone to use. There are unspoken rules about eye contact, volume, space, questions, and so forth. These conversational rules can fluctuate based on small changes in the social setting and therefore can be hard to pin down into a simple list of do's and don't's.

In the same way that multiple parts of the brain are involved with using language, multiple parts of the brain are also involved in navigating the social settings in which we use language. In social situations, the frontal lobe of the brain must shift attention rapidly between different mental tasks such as evaluating multiple sensory inputs, choosing words, and managing behavior. Furthermore, the frontal lobe must adjust word choice and tone to suit the listener. (More info on adjusting communication here.)

This constant shifting of attention can be very difficult for the autistic brain which is instead highly suited for focusing on a single mental task at a time. (Again, this is not a matter of intelligence.) The tendency to fixate on one mental task but not be able to easily switch between tasks is called hyperfocus. Hyperfocus ties together many of the social symptoms and traits of autism.

Let's look back at the list of social interaction traits from our "About Autism" page:

  • avoid eye contact while speaking or listening

    • Eye contact is difficult to varying degrees for everyone. Though most people think of eye contact as an important signal that they are listening closely or are sincere about what they're saying, the action of making eye contact - even intermittently - is taxing on the human brain. When a person maintains eye contact, their brain is continually analyzing the microexpressions on the other person's face. This uses the same parts of the brain that are needed for reasoning and critical thinking. By way of analogy, eye contact competes for the same bandwidth needed to articulate ideas. Therefore, to conserve cognitive resources and focus their attention on the conversation, the person may drop eye contact. This is especially true for some individuals with autism. 

  • seem like they are unaware of or ignoring when people speak to them even though they do respond to other sounds

    • ​Hyperfocus amplifies concentration of one line of thought often to the exclusion of any interrupting line of thought. An individual with autism may actively try to ignore interruptions to avoid the stress of switching their attention or may simply be passively unaware of events because their brain is already highly focused on something else (see our discussion on hyposensitivity in the section on behavior).

  • prefer not to be held, cuddled or touched, or might only when they initiate the closeness

    • ​Touch is one of many sensory inputs the brain receives and must process, often simultaneously with other inputs. Similar to the cognitive overload caused by maintaining eye contact, sensory input from touch can make it difficult to focus and think. There is a wide variety in the types of touch and other sensory inputs, and some types of inputs may be more distracting than others. Some sensory inputs may even give a calming effect. The types of touch and other sensory inputs that are pleasant or unpleasant vary for each individual with autism. We'll discuss this further in the section on behavior.

  • not engage in "pretend" play or imagined play - a child might not enjoy "feeding" a doll or "being" a dinosaur

    • ​​Pretend play requires multiple trains of thought to run at once. In order to pretend, a child must minimize the attention they pay to how their true self experiences the world and instead manufacture a second set of emotions, reactions, and thoughts for the role they are playing. For many children with autism, this is too much mental chaos to be enjoyable. Instead they entertain themselves with highly focused interests. They may play with the same toy in the same exact way every time, or they may learn all they can about a topic that interests them.

    • Additionally, children with autism might miss out on opportunities to practice pretend play with their peers. Children with autism tend to have a harder time learning to take turns and share than other children, and so might not attract as many playmates. 

  • struggle to relate to others' emotions

    • ​In the same way that it can be difficult for children with autism to invent emotions for imagined characters, it can be difficult for individuals of any age with autism to perceive or relate to emotions in other people. Hyperfocus may restrict some individuals with autism to focusing only on the factual information being shared in a conversation and not on the body language or tone of the other person. They might also not anticipate the emotional impact a certain question or comment might have. Similarly, sarcastic comments may be interpreted as sincere because non-literal comments require two trains of thought to run at once - one processing the words being said and one questioning how the words are used.

    • However, this does not mean that individuals with autism can't empathize. Just because individuals experience or display emotions in different ways than others might expect, doesn't mean they do not feel emotions. Furthermore, this trait might have more to do with a different condition that happens to occur more often in individuals with autism than individuals without autism (read more here).​ It may also appear that they are not relating to other's emotions because their facial expressions and movements might not match what they are saying.

  • seem uninterested in others - this might be because they are actually uninterested or because they are not sure how to communicate or interact with others

    • ​​An individual with autism might prefer to remain focused on their own thoughts because that is what a hyperfocused brain is best equipped to do. However, they might want to focus on what someone else has to say, but struggle to navigate the mental back-and-forth between actively listening and thinking about what has been said. An individual with autism may seem self-absorbed when talking to others - they might go on "too long" about a topic that is interests them but not their listener because they miss social cues given through body language. Picking up on such cues requires dividing attention between speaking and making mental checks to evaluate how they are being received.


All behavior has a purpose.

Often, people interpret the behaviors of others based on how those behaviors make them, the observer, feel. A person humming may be distracting, a person bouncing their leg may be annoying, a person rocking back and forth may be alarming. But all of these behaviors serve a purpose for the person doing them - and that purpose is never to bother the people around them. It is important to have patience with behaviors that may seem unusual and remember that there is always a reason behind any behavior.

Often, these reasons stem from how the brain processes the external and internal world. This is sensory processing. There are actually more than the 5 common senses - along with sight, sound, touch, taste, and smell, there is also tension (sensing the contraction of muscles), thermoception (temperature), equilibrioception (balance and motion, but also emotional regulation), proprioception (the sense of how the body occupies space - the "close your eyes and touch your nose" sense), and a variety of even more specific senses. Even the 5 common senses can be subdivided based on the different types of nerves responsible for sensing them. For example, touch includes texture, pressure, itch, pain, and external temperature. (Read more about autism and sensing different types of touch here.)

Senses can influence each other - most famously, smell amplifies taste. Senses also influence emotions - think of the "hangry" example (yes, hunger is a distinct sense). Senses can also dictate physical reactions, such as a smell causing a vomit reflex.

Since the brain is what processes all of this sensory input, differences in brain development determine how the brain perceives, organizes, and responds to this information.

A large part of organizing sensory input is prioritizing how much attention to pay to certain senses versus others. Think of filtering out background noise. This is easy in a library, harder in a coffee shop, and very difficult in a busy airport. As the difficulty increases, people may use strategies to help them focus, such as putting headphones on either to muffle the sound or provide a different sound to focus on. However, in a place like a busy airport headphones might not be enough because there are more distractions than just sound - there are visual distractions of people moving around, there are comfort distractions of the imperfect seats, there are emotional distractions anticipating the flight itself. This is sensory overload.

If a brain's connections make it hypersensitive to (more aware of) certain senses or all senses, sensory overload can happen in a wider variety of contexts. If sensory nerves are more easily stimulated or demand greater attention from the brain, a coffee shop might feel as chaotic as an airport - there is the taste and texture are involved in eating, scent of the coffee, volume and content of conversation, volume of coffee grinders, chatter from other tables, bodily awareness of sitting upright and bringing food and drink to the lips, tactile awareness of the furniture and clothing, and the sight of ... well ... everything. To a hypersensitive brain, these become as overwhelming as the distractions in the airport, and fluidly shifting attention between these different sensory inputs can be extremely difficult.

As we discussed in the section on social interactions, the autistic brain is highly suited for focusing on a single mental task as once. To help them focus when faced with a barrage of sensory input, they may use external strategies that "self-stimulate" specific senses. Using these strategies is called "stimming." (In a person without autism, it would probably just be called fidgeting.) Stims can range from those common among people with and without autism (twirling hair around fingers, cracking your knuckles or other joints, drumming fingers, jiggling a leg or foot, humming, squeezing a stress ball, etc.) to those more characteristic to people with autism (rocking the body, flapping hands, bouncing, jumping, twirling, pacing or walking on tiptoes, pulling hair, rubbing the skin or scratching, turning a light switch on and off repeatedly, staring at rotating objects such as ceiling fans, sniffing at objects, repeating words or phrases, rearranging objects).

These strategies are also used by individuals to provide more sensory input when there isn't enough. Just as some brains are hypersensitive, others are hyposensitive, meaning that their perception of their senses is already muffled. Having not enough sensory input can be just as distracting as having too much. Think again of the common strategy of using headphones to block out sound, but consider that some people listen to headphones when working in a place that is already quiet. They provide their ears with something to focus on so that their brain isn't distracted by the need to searching for the faintest sound.

The same environments that pose challenges to hypersensitive brains can also challenge hyposensitive ones. For example, a hyposensitive person might love the sounds and smells of a coffee shop but still find it uncomfortable because their decreased bodily awareness might cause them to spill a drink or bump into others.

It is very possible and very common to be a combination of hyper- and hyposensitive with different senses affected differently. Also, not all stimuli are equally pleasant. For example, some textures might be highly desirable while others are very unpleasant. All brains perceive things differently.

​Additionally, it may be difficult for some individuals, especially children, to articulate what specific sense is causing distress if it is not one of the 5 common senses. For example, a weighted blanket can be very calming, but it is hard to explain this need because most people take their sense of pressure for granted.

In the past, stims such as hand flapping that were seen as more disruptive were strongly discouraged in autism treatment, but it is important to remember that such behaviors serve a purpose. Assuming that these behaviors mean the individual is not paying attention or does not care about bothering others unfairly elevates the sensory needs of the observer. Excessive or potentially harmful stims can be channeled into more positive stims, but inhibiting stims without replacement strategies is not helpful.

Behavior is communication. Consider what is being communicated by the behavioral traits from our "About Autism" page:

  • have heightened sensitivity to sounds, smells, or textures - they might have unusual reactions to how things feel, taste, smell, or sound​​

  • repeat actions including motions, sounds, and words

  • engage in activities that stimulate their senses such as making noises, flapping their hands, or rocking their bodies

  • fixation on sensory experiences they find enjoyable

  • have difficulty adapting to changes in schedule - this is more than just disappointment; they experience stress even if they would normally enjoy a certain activity

    • The brain prepares itself for certain stimuli and must use extra energy if different stimuli appear instead. (This is why watching a series of different, rapidly flashing images is mentally tiring whereas watching a movie made of  very similar, rapidly flashing images is not tiring.)

    • Also, structured activities and routines reduce stress for people with autism because then they do not need to divide their attention between what they are doing and figuring out what may be about to happen next. This relates to the trait of hyperfocus discussed in the section on social interactions.


Many of the things we have already discussed feed into how a child learns. Externally, their ability to process and produce language, their ability to interact with others, and their ability to manage sensory needs all influence how fluidly they can navigate the requirements of a classroom. Internally, the developmental differences in the brain which govern these abilities  also leads to differences in learning.

The spectrum nature of autism holds just as true here as with the other trait areas already discussed. An individual may be very skilled in one type of mental task and not as skilled in another. It is important to avoid assumptions about an individual's receptive language skills (their ability to hear, understand, and perform other cognitive tasks related to language) based on their expressive language skills (their ability to communicate verbally using typical grammar). It is important to avoid assumptions about an individual's emotional awareness based on their social behaviors. And it is important to avoid assumptions about an individual's academic abilities in connection with any of their other traits.

Additionally, children with autism develop different skills at different rates. They may have delays in cognitive skills, while their ability to walk and move around are about the same as other children their age. They might also master a difficult skill before they learn an easy one even if these skills seem related. For example, a child might be able to read long words but be unable to identify what sound a "b" makes.

Let's look back at the list of learning traits from our "About Autism" page:​

  • a child might not point at objects or might not follow with their eyes when someone points to something

    • This connects back to hyperfocus - if the object being pointed to is not what they want to pay attention to, they won't engage.

  • a child might lose skills they once had (such as loss of vocabulary*)

    • This is perhaps one of the most frustrating symptoms for parents. A regression of skills is upsetting and perplexing because it seems counterintuitive that a young brain can unlearn simple skills. The physiological cause of this regression is not well understood, though it may tentatively be connected to incorrect neuron migration and synaptic pruning as the brain develops. In utero, neurons of different types must travel or "migrate" from their origin locations within the brain to multiple areas across the brain. In early childhood, many synapses (connections between neurons) form. In late childhood, many of these synapses are "pruned" or removed to improve the efficiency of other synapses that are left in place. Further studies are required in order to say with certainty if delays in migration is a causal factor of autism or if incorrect pruning contributes to skill regression, however two recent, not-yet published studies add credibility to this connection.

    • *About 25%–30% of children with ASD have some words at 12 to 18 months of age and then lose them. (Johnson, C.P. Early Clinical Characteristics of Children with Autism. In: Gupta, V.B. ed: Autistic Spectrum Disorders in Children. New York: Marcel Dekker, Inc., 2004:85-123.)

  • delayed language development

    • Typical language development occurs at a fairly predictable pace and order, though there are many reasons why a child might deviate from standard milestones. Autism is one of these reasons, though children with autism may also develop language at a completely typical or even advanced pace. Differences may involve delays in reaching milestones, reaching later milestones before earlier ones, repeating whole phrases they've heard (echolalia), or never producing spoken language (being nonverbal).

    • Because many traits of autism involve difficulties with social interactions, children with autism may have fewer opportunities to practice their language skills. Techniques such as modeling, playing, and creating situations that encourage their use of language can help provide meaningful, motivating opportunities to practice their language skills. Strategies can include putting a favorite toy out of reach so that they are encouraged to ask for it, reading a book together and comparing thoughts about each page, narrating your actions, and verbalizing their gestures (if they lift a package for you to open, you can say “help” or “open please”).

  • delayed cognitive or learning skills

    • This stems from differences in brain development, but may be somewhat compounded by a mismatch between the learner's needs and the learning environment. For example, a classroom which causes sensory overload or mishandles stimming presents an additional "focus" hurdle to learning the curriculum. More subtly, social discomfort of children with autism who want friends but are unsure how to develop friendships can add to the stress of a social learning environment.

  • may have obsessive interests and learn everything they can about a certain subject

    • This one is a bit subjective. Being passionate about a topic is not strictly a symptom of autism. Many children and adults with and without autism are passionate about certain topics. Hyperfocus tendencies and difficulties navigating social interactions may simply highlight the passions of individuals with autism. Because of the focused attention individuals with autism can dedicate to something, they will be able to build a rich knowledge of a preferred topic. Because they may struggle to keep a conversation balanced between their interests and their listener's, their knowledge may seem "obsessive."

Additional Symptom Connections

Because of the interconnected nature of the human body, systems that seem separate from the brain are in fact also affected by how the brain develops. Individuals with autism commonly have issues with digestion and sleep cycles. Sensory sensitivity may influence which foods they prefer, and they may appear to be picky eaters because so few foods are palatable to them. Their limited diets may not align with what is best for digestion resulting in constipation or other digestive issues. The same digestive issues may also be caused by other factors. The research data in this area is so far rather sparse. Insomnia and a lack of deep sleep may be the direct result of a hyperfocused brain, connected to digestive issues, or caused by other factors. A lack of sleep can in turn exacerbate other symptoms of autism, particularly ones related to behavior, social interactions, and learning. This article gives a very clear overview of these interconnections.

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